<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>固定定位</title>
    <style>
        .l{
            height: auto;
            bottom: 0;
            left: 50px;
            position: fixed;
        }
        .r{
            height: auto;
            bottom: 0;
            right: 50px;
            position: fixed;
            
        }
        .box{
            width: 70%;
            height: auto;

            position: relative;
            margin: 15px auto;
        }

        #back{
            width: 50px;
            height: 120px;
            background-color: orange;

            position: fixed;
            bottom: 0;
            right: 0;
            text-align: center;
            padding-top: 30px;
        }
    </style>
</head>
<body>
    <!-- 锚点 -->
      <div class="l">
        <img src="./img/ad-l.png" alt="">
    </div>
    <div class="r">
        <img src="./img/ad-r.png" alt="">
    </div>
     
    <a id="top"></a>
    <div class="box">
        <img src="./img/box.png" alt="">
    </div>
    <div id="back"><a href="#">回<br>到<br>顶<br>部</div>
</body>
</html>